The present invention relates to a piezoelectric transformer and, more particularly, to a multi-layer piezoelectric center-drive ceramic transformer, in which inner electrode layers of input terminal electrodes are alternatively arranged in different polarities to enhance xc2xd wavelength resonant mode and to eliminate full-wavelength resonant mode, so as to improve the efficiency of conversion to over 95%.
Early in 1956, doctor C. A. Rosen reported a study about a transverse type transformer, namely, the so-called Rosen-type transformer. FIG. 1 shows a Rosen-type transformer. This structure of Rosen-type transformer comprises a narrow, elongated ceramic plate, which is divided into two halves subject to the arrangement of its electrode means (direction of polarity). To a boosting transformer, the driver (input) is formed by: covering a silver electrode on one half of the top side as well as the bottom side along the direction of the length to work as an AC input end. The polarity P extends along the direction of the thickness (of low impedance). The other half (small silver electrode surface area) is the generator, where the silver electrode area is disposed at the end edge to work as an output end. The polarity of the generator extends along the length (of high impedance). Under this transverse-type transformer, when the frequency at the AC input end is equal to the resonant frequency in the direction of the length of the transformer, the transformer is caused to produce a mechanical resonance, i.e., the reverse piezoelectric effect (electric energyxe2x86x92mechanical energy) causes a vibration along the direction of the length, and the mechanical resonance is converted into a voltage at the generator for output due to forward piezoelectric effect. Because the length of the ceramic plate is greater than its thickness, the impedance at the output end (generator) is constantly greater than the input end (driver), and a boosting effect is produced.
Further, because of the resonant effect of the piezoelectric ceramic plate is produced under full-wave frequency, half-wave frequency, as well as {fraction (3/2)}-wave frequency, the boosting working can be classified into half-wave mode, full-wave mode, and {fraction (3/2)}-wave mode. An apparent boosting effect is seen at every mode frequency. Full-wave and half-wave resonant modes are most commonly adopted. More particularly, the frequency of 40 Kxcx9c60 KHz for driving a CCFL (cold cathode fluorescent lamp) is based of half-wave mode. During application, a piezoelectric ceramic transformer provides a single resonant mode only to save energy consumption and to obtain better efficiency of conversion. By means of electrode design and support arrangement, a better single mode resonant effect can be achieved to greatly improve the efficiency of conversion.
The boosting ratio of a piezoelectric ceramic transformer is directly proportional to the L/T (length/thickness) ratio of the ceramic plate. When increasing the boosting ratio, the ceramic plate must be made relatively thinner or relatively longer. However, the ceramic plate tends to break when made relatively thinner, or becomes not applicable when made excessively long. In recent years, different multi-layer ceramic fabrication techniques have been well developed for the fabrication of laminated ceramic capacitors, laminated ceramic conductors, laminated ceramic resistors, and the like. By means of the application of a similar laminated ceramic fabrication technique, the size of a single-layer ceramic transformer can be reduced to ⅓. Because the thickness of each individual layer is greatly reduced, the boosting ratio is relatively increased. A laminated ceramic transformer can be used in the fields that require high boosting ration and small installation space (for example, digital camera, thin type notebook computer, or the like). The invention is developed by means of the application of laminated ceramic fabrication techniques.
It is one object of the present invention to provide a multi-layer center-drive piezoelectric transformer, which employs a multi-layer ceramic sintering technique to sinter a stack of ceramic blanks into a solid member for making a multi-layer center-drive piezoelectric transformer. It is another object of the present invention to provide a multi-layer center-drive ceramic piezoelectric transformer, which keeps inner electrode layers of input terminal electrodes alternatively arranged in different polarities to enhance xc2xd wavelength resonant mode and to eliminate full-wavelength resonant mode, so as to improve the efficiency of conversion to over 95%. The multi-layer center-drive ceramic piezoelectric transformer comprises A multi-layer center-drive piezoelectric transformer comprising a plurality of piezoelectric ceramic blanks sintered in a stack, the piezoelectric ceramic blanks each comprising a top cover layer, a bottom cover layer and an odd-number layer and an even-number layer sandwiched in between the top cover layer and the bottom cover layer, first and second inner electrode layers of reversed polarities respectively printed on the odd-number layer, third and fourth inner electrode layers of reversed polarities respectively printed on the even-number layer, first and second output terminal electrodes respectively printed on two distal ends of the odd-number layer and even-number layer of each piezoelectric ceramic blank, and first and second input terminal electrodes respectively printed on two opposite lateral sides of each of the odd-number layer and even-number layer of each piezoelectric ceramic blank, the first input terminal electrodes of the odd-number layer and even-number layer of each piezoelectric ceramic blank being respectively connected to the first inner electrode layers and the third inner electrode layers, the second input terminal electrodes of the odd-number layer and even-number layer of each piezoelectric ceramic blank being respectively connected to the second inner electrode layers and the fourth inner electrode layers.